Last weekend I built world and install a new kernel and booted.
(My previous build was from 1/15.)  Obviously, a few things did
not work when I booted and I had to MAKDEV wscons and mung the /etc/ttys
file -- no big deal.  But is there any way that this could happen automatically
for the niave user?  Perhaps the wsdevice could smash itself into the 
cdevsw at the ttyv0 slot and then print out a warning if it were referenced
thru that major.